Nowadays, a belt pulley set is widely used in modern office automation equipment, industrial equipment or measurement equipment for transmitting the inner mechanical components. For example, a multifunction peripheral with multiple functions in one structural unit includes a belt pulley set to drive corresponding components for performing the printing, faxing or scanning operation.
Referring to FIG. 1, a schematic cross-sectional view of a conventional multifunction peripheral is illustrated. The multifunction peripheral 1 principally includes a main body 11 and a belt pulley set 12. The belt pulley set 12 is disposed inside the main body 11. The belt pulley set 12 includes a driving pulley 121, a follower pulley 122, a belt 123 and a tension pulley 124. The belt 123 is made cyclic and encloses around the driving roller 121 and the follower roller 122. The driving pulley 121 is driven by a power source (e.g. a motor) to rotate. By means of the belt 123, the follower pulley 122 is synchronously rotated with the driving roller 121.
As known, for steadily running the belt pulley set 12, it is necessary to provide sufficient tension force to confine the belt 123 of the tension pulley 124. During the process of inverting the driving roller 121, tension forces are differentially exerted on the sides A and B of the belt 123. Please refer to FIG. 1 again. When the driving roller 121 is rotated in an anti-clockwise direction, a tight-side tension and a slack-side tension are exerted on the sides A and B, respectively. Under this circumstance, a length change is resulted on the side B of the belt 123 and thus the tension force of the belt 123 is insufficient. As a consequence, the precision of feeding the document is reduced and the scanning quality is deteriorated. For providing sufficient tension force to confine the belt 123 and adjusting the length change, the tension pulley 124 is usually arranged on the slack side B of the belt 123.
Since only one tension pulley 124 is arranged on the slack side B of the belt 123, single-side tension adjustment is allowable when the belt pulley set 12 is rotated in a single direction. Nowadays, as the multifunction peripheral has duplex scanning capability to scan or print both sides of the document, the belt pulley set 12 needs to rotate in either the anti-clockwise direction or the clockwise direction. In other words, the slack-side tension is exerted on the side B of the belt 123 when the driving roller 121 is rotated in the anti-clockwise direction, but the slack-side tension is exerted on the side A of the belt 123 when the driving roller 121 is rotated in the clockwise direction. The belt tension adjustment mechanism with the single tension pulley 124 fails to effectively adjust the tension force of the belt 123 in both of the anti-clockwise direction and the clockwise direction. Therefore, the problems of causing low document-feeding precision and deteriorated scanning quality still exist when the multifunction peripheral 1 performs the duplex scanning operation.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop a belt tension adjustment mechanism according to the present invention through wholehearted experience and research.